The present invention relates to an image forming apparatus, such as a copying machine or a facsimile machine, having a multiple image forming capability to perform a double-sided image transfer or combined image transfer operation, for instance, as well as to a paper return device which is added to an image forming apparatus to give it the multiple image forming capability.
In one previous approach to realizing the multiple image forming capability in a copying machine, one side of each sheet of a document is successively copied, individual sheets of copying paper, each carrying a reproduced image on one side, are stacked as if in a stock, and then the other side of each sheet of the document is successively copied. This approach is known as a stock method. In another previous approach known as a non-stock method, two sides of each sheet of a document are copied in succession on two sides of each sheet of copying paper before copying on a succeeding sheet of copying paper.
In one known example of a non-stock type copying machine, a sheet of paper carrying an image reproduced on one side in an image forming section provided inside a main body of the copying machine is ejected through a paper output port, which opens to the outside of the main body of the copying machine, the ejected sheet is transferred to a paper return slot formed in the main body of the copying machine by a reversible paper transport unit which is detachably fitted to the main body, and the sheet reentered from the paper return slot is fed again to the image forming section through a refeeding path. In this construction, it is possible to provide a paper refeed mechanism for double-sided copying operation in the form of the reversible paper transport unit which is detachably fitted to the main body of the copying machine. This means that the aforementioned construction makes it possible to provide a double-sided copying mechanism as an optional unit and thereby increase the ease of maintenance.
Today""s copying machines are mostly of a type that accommodates paper trays in their main bodies. The majority of this type of copying machines also have manual feed trays for loading sheets of paper to be fed directly from outside their main bodies to permit manual paper feed as is the case with the aforementioned conventional copying machines.
As will be noted from the above discussion, a conventional copying machine having the aforementioned construction usually has two paper paths for feeding paper to an image forming section from outside a main body of the copying machine. These are a refeeding path for feeding the paper transferred by a reversible paper transport unit and a manual feeding path for feeding individual sheets of paper loaded on a manual feed tray. A problem of this conventional structure is that the provision of more than one paper path for a similar purpose leads to inefficient use of available space and an increase in equipment cost.
One potential approach to achieving improved space utilization efficiency and cost reduction would be to construct a reversible paper transport unit in such a way that a paper output port of an image forming apparatus, such as a copying machine, is connected to its manual feeding port when the reversible paper transport unit is fitted to the apparatus. This construction will make it possible to use a paper return slot also as a manual feeding port and thereby combine multiple paper paths for feeding paper from outside a main body of the apparatus to an image forming section provided inside the main body into a single path.
The aforementioned conventional copying machine having two paper paths, i.e., the refeeding path and the manual feeding path, is constructed such that paper refeed means (feed roller) is caused to automatically start feeding a sheet of paper, which has been transferred by the reversible paper transport unit to the paper return slot, when an original is fed automatically, for instance, and manual feed means (feed roller) is caused to start feeding a sheet of paper each time a start button is pressed, for instance, when the paper is loaded on the manual feed tray.
If conventionally separate paper paths for feeding the paper from outside the main body of a copying machine to its image forming section provided inside the main body is combined into a single path by employing the aforementioned reversible paper transport unit which connects the paper output port to the manual feeding port when fitted to the copying machine, the same paper feed means (feed roller) is used for both manual paper feed and double-sided copying operations. Accordingly, when a sheet of paper has been fed from the reversible paper transport unit during double-sided copying mode, operation of the paper feed means must be controlled in a different way from manual paper feed mode.
It is therefore an object of the invention to achieve improved space utilization efficiency and cost reduction by combining multiple paper paths for feeding paper from outside a main body of an image forming apparatus to an image forming section provided inside the main body into a single path and to provide an image forming apparatus capable of properly controlling means for feeding the paper along the combined paper path in a double-sided copying operation.
According to the invention, an image forming apparatus comprises a main body, an image former provided inside the main body of the apparatus for forming an image on paper, a paper feeding port formed in the main body of the apparatus opening to its outside, a paper feeder for feeding paper inserted into the paper feeding port toward the image former, a paper ejector for ejecting the paper carrying the image formed by the image former to the outside of the main body of the apparatus through a paper output port formed in the main body opening to its outside, a paper sensor which senses the paper inserted into the paper feeding port and outputs a paper sensing signal, a driver for driving the paper feeder, a paper return device for feeding the paper ejected from the paper output port back to the paper feeding port, a discriminator for judging whether the paper return device is in an operating condition, and a paper feed controller for controlling the driver so that the paper feeder initiates a paper feed operation when the paper sensing signal is output while the paper return device is in its operating condition.
In this construction, when performing a double-sided copying operation, for instance, a sheet of paper ejected from the paper output port of the main body of the apparatus carrying an image on one side only is returned to the paper feeding port and fed again to the image former from the paper feeding port. Accordingly, it is not necessary to provide a dedicated paper path in the apparatus for refeeding the paper. This makes it possible to combine conventionally separate paper paths from outside the apparatus to its internal image former into a single path, and eventually achieve improved space utilization efficiency and cost reduction.
It is also possible to properly perform the paper feed operation by using the paper feeder even when the paper return device is in its operating condition by causing the paper feeder to initiate the paper feed operation when a specified period of time elapses from the time the paper sensing signal is output from the paper sensor.
These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings.